The long term objectives of this proposal are to understand the developmental mechanisms which give rise to the organization and function of sensory maps in the nervous system. The focus of this work is on the possible role of regulative plasticity in the adaptations of sensory maps to growth of the organism or to environmental influences. The goals are to understand the functional organization of a topographically mapped sensory system, and to determine the mechanisms which regulate and refine the tuning of interneurons within the sensory maps to the relevant sensory stimuli. These questions will be studied in a relatively simple insect system, the cricket cercal sensory system, in which both the primary afferents that comprise the map and the primary interneurons that "interpret" the map are well characterized. The specific aims of this proposal are to describe the structural and functional organization of this system and to determine whether activity- dependent mechanisms are involved in either the formation or the fine tuning of this topographic map. Using this preparation, the cellular mechanisms underlying the structural organization, function and short term regulative plasticity of the system can be analysed at the synaptic, cellular, and systems levels. The system will be analyzed anatomically using a computer-based neuronal reconstruction system to construct a stereotaxic atlas of the topographic map, and a confocal microscope to observe the localization of activity- dependent dyes. A combination of extracellular and intracellular recording techniques will be used to study the system physiologically as it develops and to test the effects of rearing animals in specific sensory environments. This research will lead to a better understanding of the organization and function of sensory systems in general and the developmental mechanisms involved in their growth and adaptations to the environment in which they develop.